1. Field of the Invention
The present invention is directed to medical catheters, and specifically directed to a variable diameter catheter (VDC) in which the diameter of the catheter is decreased for insertion into a body cavity.
2. Description of Prior Art
Catheters are ubiquitous to the medical field, finding importance in a variety of uses. The term "catheter" is commonly used to identify a tubular instrument that is inserted into various body cavities, naturally or surgically opened, and the catheter of the present invention will be understood as intended thus broadly unless the context clearly indicates the contrary. The following list indicates the broad range of uses for catheters:
1. intravenous cannula PA1 2. umbilical catheters PA1 3. endotracheal tubes PA1 4. suction catheters PA1 5. oxygen catheters PA1 6. stomach tubes PA1 7. feeding tubes PA1 8. lavage tubes PA1 9. rectal tubes PA1 10. urological tubes PA1 11. irrigation tubes PA1 12. trocar catheters PA1 13. heart catheters PA1 14. aneurysm shunts PA1 15. stenosis dilators
The use of catheters has been recorded from as early as 3000 B.C. An interesting history of eary catheter use may be found in an article by Roy A. Tucker entitled "History of Sizing of Genitourinary Instruments", Urology, September 1982, Vol. XX, No. 3, pages 346-349. The earliest catheters were metal tubes generally comprising one or two distinct sizes, depending upon the size of the patient. Catheters such as these were found in the ruins of Pompeii, which were buried in 79 A.D. The development of the modern catheter has been accredited to Lorenz Heister (1683-1758), who made the catheter in the shape of the natural curve of the prostatic urethra. Benjamin Franklin, famous statesman, journalist an scientist, has been accredited with inventing a urethral catheter for use by his brother, a victim of prostatic obstruction.
Perhaps the most significant achievement in the field of catheter design to date is ascribed to the development of the Foley catheter, which was invented around 1945 by Dr. Frederick Foley. This catheter is still very active in the urological market. The Foley catheter is a somewhat rigid latex or plastic tube, which is inserted in the urethral tube optimally by means of a stylet. The stylet is similar in appearance to an opened coat hanger wire. The stylet is placed within the catheter tube, thus allowing some rigidity with the tube is being inserted into the urethral tube. Prior to the development of the Foley catheter, there existed the problem of the patient unconsciously pulling the catheter tube out of the urethra or out of the bladder. The Foley design includes a tube with an inflatable cuff or balloon at the distal end of the catheter so as to hold the catheter in place. The distal end of the catheter shaft is inserted into the patient's urethra during placement, and the shaft is passed through the urethra until the portion of the catheter comprising the balloon is located in the bladder with the proximal end of the catheter located outside the patient's body. The balloon is then inflated in order to retain the catheter in the bladder. During catheterization, urine drains from the bladder through a drainage lumen in the catheter and through a drainage tube connected to the catheter into a drainage bag for collection therein.
Other types of catheters include one developed by Peterson and disclosed in U.S. Pat. No. 3,490,457, which is directed to a catheter inserted into a bladder or other body cavity through a small opening. When the Peterson catheter is in place, a thin, elastic outer sleeve is flexed to fold out a set of radially projecting wings, which prevent the catheter from slipping out of position when in use.
U.S. Pat. Nos. 4,467,790 to Schiff, 4,276,874 to Wolbek et al, and 4,406,656 to Hattler et al are all directed to catheters for intra-aortic use. Schiff is directed to an intra-aortic percutaneous balloon catheter of reduced diameter. A stylet extends through the balloon catheter and is anchored to the catheter tip. The stylet's proximal end is coupled to a control knob assembly which, when twisted, twists the stylet in the tip, causing the balloon to be twisted as it is being lengthened. The lengthening of the balloon prevents the balloon membrane from doubling up as it is twisted. The twisting operation significantly reduces the exterior balloon diameter, enabling the balloon to fit through a small diameter percutaneous sheath inserted into the artery. This causes a blood-type seal, preventing blood from exiting the sheath. Hattler et al are directed to a multi-lumen catheter adapted to be inserted into the vein of a patient through a conventionally-sized insertion needle. The collapsible lumen expands outwardly under the pressure of fluid flow. When fluid flow is absent, the lumen collapses to a smaller cross-sectional area. Wolbek et al are directed to an elongatable balloon intra-aortic catheter.
U.S. Pat. Nos. 4,493,711 to Chin et al, 4,195,637 to Gruntzig et al and 4,315,512 to Fogarty are directed to catheters for use in dilating a stenosis or occlusion in a body passageway. Chin et al are directed to a tubular extrusion catheter which provides a means for placement of a soft, non-elastomeric tube through the lumen of a normal or occluded artery, vein or other body passageway. Gruntzig et al are directed to a dilatation catheter in which the outer wall of the catheter is collapsed over an inner support hose. Once installed into the body, the lumen of the catheter is filled with a solution to expand the wall. Fogarty is directed to an elastomeric dilatation balloon catheter which is placed in an occluded section of a blood vessel. The balloon is expanded through the injection of a volume of fluid into the catheter, thereby pressing the occlusion against the wall of the blood vessel, which subsequently removes the occlusion.
The following patents are directed to catheters of varying sizes. U.S. Pat. No. 4,401,433 to Luther is directed to folding a catheter tube in order to reduce its overall size. The catheter is folded by means of arms connected to a catheter folding device as the catheter advances into the device. The folded catheter enters a cannula, which is then inserted into the patient. The preferred shape of the catheter is elliptical and, when properly folded, the catheter is said to have a small cross-sectional area. German Pat. No. 1,810,804 to Metz is directed to the use of a folded catheter in a cannula. Metz employs a "physiological adhesive" to secure the catheter in place. U.S. Pat. Nos. 4,141,364 to Schultze and 4,460,541 to Doherty both disclose balloon-type tubes, wherein the tube is collapsed for insertion and then inflated.
Newman et al, in an article entitled "A General Ureteral Dilated-Sheathing System", Urology, Vol. XXV, No. 3, March 1985, pages 287-288, suggest a dilator-sheathing system which consists of four coaxial Teflon (Reg. TM) catheters with external dimensions of 6, 10, 14 and 17 French. The term "French" is well known to the catheter art as an increment of measurement of the diameter of a catheter. To facilitate passage, the larger catheters are tapered on the dilating end so that they approximate the size of the next smaller catheter. In operation, the 6 French (6-F) catheter is advanced to a designated point in the ureter. Then, the 10-F is advanced over the 6-F catheter, and so forth until the 17-F catheter is in place. The three smaller catheters are then removed, leaving the 17-F catheter in place. In this manner, the size of the ureter is gradually increased, which, in theory, reduces trauma to the mucous membranes.
Summarizing the state of the present-day catheters, there are a number of types of catheters in use today. However, it appears that the Foley-type catheter and its variations are predominant in the medical technology market. According to a Frost and Sullivan report, entitled Prepackaged Kits and Trays-Markets in the U.S. (#A1139), copyright 1983, "[T]here are more Foley catheter care trays sold than any other single trays or kits. This reflects the common need to catheterize both hospital patients and nursing home residents". However, recent studies in these types of catheters have placed doubt on their effectiveness. Problems, such as infection, inserting the wrong-sized catheter, leakage, and difficulty in insertion, create a plethora of hazards in the catheter industry.
According to Calvin M. Kunin, M.D., in an article entitled "Genital Urinary Infections in the Patient at Risk: Extrinsic Risk Factors", The American Journal of Medicine, May 15, 1984, pages 131-139, catheter-induced infections are the most frequent and intractable problem in hospital infection control. Approximately 35% of all nosocomial infections are related to the urinary tract. When used inappropriately, catheters can introduce microorganisms into the bladder and impair host defenses sufficiently to produce infection of the urinary tract. The urethral catheter drains the bladder, but exerts pressure on the mucosa and obstructs the periurethral ducts.
It is also suspected that many of the infections that are caused as a result of an operation come from catheter infections. In most cases, these are not documented, as they are merely passed off as a "post-operative infection".
A study published in a recent issue of the New England Journal of Medicine and reported in the Frost and Sullivan report (supra) at page 32, suggests that if the author's sample was expanded nationwide, 56,000 deaths per year might be associated with Foley catheter-related infections. This represents approximately 75 of every 10,000 patients who recently underwent the urological catheterization procedure at short-term general admission hospitals and implies that 14% of all catheterized patients in those hospitals die regardless of cause.
It is believed that one of the major difficulties associated with catheter-induced infections results from the absence of accurate sizing methods being available for insertion through the urethral tube, as sizing generally is the result of "on-site inspection". In other words, the physician or medical technician usually determines what size catheter the patient needs by observing the anatomy of the patient. For example, pediatrics generally require an 8-F to 10-F sized catheter, while a normal adult requires a 16-F to 20-F sized catheter. It is logical to assume that an underestimation results in urine or other body fluid leakage, while overestimation results in trauma to the urethal tissues.
Other difficulties result from the actual insertion of the catheter. Because catheterization has become a fairly standard procedure in medicine today, the insertion process is now generally handled by hospital staff personnel other than physicians. Unless the technician has the requisite skill for inserting a catheter, the insertion process can be rather difficult, resulting in the overhandling of a catheter which can precipitate catheter-induced infections.
While catheterization is documented to be the cause of many infection-related problems associated in the medical industry, it is still considered to be the lesser of two evils. On the one hand, if the physician does not catheterize a patient, the patient may be exposed to uremic poisoning or a burst or tear in the bladder. Because catheters are readily available and very common, a physician will undoubtedly insert a catheter and risk the resulting infection.